(a) Field of the Invention.
This invention relates to temperature measurement by thermocouple means and more particularly to the provision of a simple but effective adjustable thermocouple mounting for use in positioning a thermocouple in proper position for detecting temperatures within a machine.
(b) Description of the Prior Art.
Thermocouple type temperature sensors are widely used in industry. One frequent use is for detecting or monitoring the temperature of the interior of a machine such as a plastic working or extrusion machine, as distinguished from measurement of the surface temperature. For such use an opening is usually drilled or otherwise formed in the machine and a temperature sensor such as a thermocouple is inserted into the opening. In order to measure the temperature of the machine itself at such point and not merely the temperature of the air in the opening surrounding the thermocouple it is desirable to contact the temperature detecting end of the thermocouple with the wall of the opening, usually the bottom wall or closed end of a drilled opening. Since the thermocouple is usually rather fragile, it is also usually the custom to contain the thermocouple in a protective tube the end of which is then pressed against the bottom of the detection orifice, i.e. the opening in the machine for the thermocouple.
Various means for mounting the thermocouple in the detection orifice have been made in the past by which the thermocouple may be adjusted in the detection orifice and maintained constantly against the bottom of the orifice. Exemplary of such mounting means are those shown in U.S. Pat. Nos. 3,468,723 to W. Lambert and 3,679,490 to R. R. Finkbiner. In these mounting devices a bushing is threaded into the upper portion of the thermocouple opening, or detection orifice. The opposite or outer end of the bushing is provided with a coupling pin arranged to interact with a cap designed to be placed over the outer end of the bushing and with which it interlocks in a so-called bayonet-type interlock. The interior of the cap is desirably threaded for engagement either with a spiral spring wound about the thermocouple covering as shown in the Lambert patent or with the spirals of a resilient spiral armor about the surface of the thermocouple cable as shown more particularly in the Finkbiner patent. When the thermocouple is mounted in the detection orifice, or well, in the machine it is pressed forcibly against the bottom by the compression of the spring or resilient armor by engagement of the bayonet-type cap with the upper or outer end of the bushing threaded into the machine, the body of the thermocouple having been first adjusted within the threads of the cap to extend a suitable length beyond the cap for compression against the bottom of the thermocouple orifice or well.
An alternative arrangement has been suggested in U.S. Pat. No. 4,259,123 to J. Tymkewiecz who in one embodiment uses the usual bayonet cap-type arrangement, but in a second embodiment eliminates the bayonet cap and instead inserts an external thermocouple spring through a restricted orifice in the top of the bushing threaded into the machine element. The spring is provided with a spiral in the opposite direction from the direction of the threads on the bushing which engage with threads in the machine. When inserting the thermocouple in the machine the bushing is first adjusted along the thermocouple by engagement with the sprial spring so that the thermocouple extends from bushing the same distance as the distance from the top to the bottom of the detection orifice into which it is to be inserted. The bushing is then threaded into the machine until the thermocouple engages the bottom of the temperature orifice in the machine. The opposite spiral of the spring prevents the thermocouple from backing off in the bushing as the bushing is engaged with the bottom of the temperature orifice and insures intimate engagement of the end of the thermocouple with the bottom of the temperature orifice.
It has been considered necessary by those skilled in the art for effective compression to be applied to the thermocouple for it is to be essentially positioned at the correct position and then compressed by engagement of the cap or bushing in which the thermocouple is effectively held with the top of the bushing already threaded into the machine or with the threads of the temperature orifice in the machine whose temperature is to be measured. There have been other suggestions for mounting thermocouples for detection of the interior temperature of machines, but substantially all have, so far as the present inventor is aware, at least where interengaged threads are used, followed basically the same principles as the Lambert and Finkbiner patents in requiring preadjustment of the length of the thermocouple extending beyond a fitting, followed by securing of the fitting or a portion thereof in position such that the thermocouple section is compressed against the bottom of the thermocouple well or orifice. While effective in accomplishing their purpose such prior devices have had certain drawbacks including undue complication and expense for the ends to be attained, particularly in the case of the use of bayonet-type fittings, and possible excess compression of the thermocouple with resultant damage and cocking in the temperature orifice, particularly, in the absence of a bayonet cap-type fitting. Excess force on the end of the thermocouple can damage the thermocouple or its cable and cocking of the thermocouple can not only damage it, but prevents proper contact with the bottom of the detection orifice.